In order to provide adequate power in the normal automobile for acceleration and grade ascension under heavily loaded conditions and at all altitudes and temperatures, the internal combustion engine which is provided is much larger than is necessary for most driving conditions. For example, most automobiles average about 30 miles per hour speed over their entire lifetime, at which speed only about 5% of the maximum available power is required. On the other hand, this same vehicle averages about three stops for every mile driven, so the higher start and acceleration power is needed.
It has been know to those experienced in the field of internal combustion engines, that a significant loss of efficiency occurs when the full air and fuel charge is burned under conditions where serious heat losses to the relatively cool cylinder walls occur. It is also well known that satisfactory ignition and burning of the fuel-air mixture occurs only within certain definite mixture ratio and limits, and that for air and gasoline this ratio is from about 5:1 to about 20:1, on a weight basis. Further, to a first order of approximation, this ratio is independent of the pressure of the gas. In present engines, engine power is reduced by reducing the inlet charge density, or the pressure, while keeping the mixture ratio combustible, within the limits noted above. This inlet "throttling" causes the engine cylinders to intake air below atmospheric pressure and to discharge it at full atmospheric pressure, thereby incurring a "pumping loss." This is a serious cause of inefficiency except under full load conditions.
Classic analysis of engine thermodynamics also indicates that heat loss out the exhaust can be minimized when the peak combustion temperatures are kept relatively low.
To eliminate the "pumping loss" inherent in throttling action when air is taken in to the cylinders at less than atmospheric pressure, and to reduce the combustion heat losses to the cylinder walls at less than maximum power output, many efforts have been made in the past to operate an engine such that a full air charge is used each cycle (thereby minimizing the pumping losses by taking air into the cylinder at atmospheric pressure) with the reduced fuel quantity inserted into the air charge so as to mix with only a portion of it, to locally maintain a suitable mixture ratio. The so-called "stratified charge" engines represent one of the efforts along these lines.
To date, these types of engines have not been entirely successful because ignition is not assured over the widely varying conditions encountered in an automobile engine, and in view of other problems. In general, the exhaust emissions characteristics of such engines are as good or better than conventional engines and the fuel economy is markedly better, but their "drivability," or the engines ability to operate a vehicle under widely varying load and speed conditions, is unacceptable.
Objects of the present invention therefore include the following for an engine under less than full power: (1) the reduction of heat lost to the combustion chamber walls, including the sidewalls and the top of the cylinder; (2) reduction or elimination of "pumping load" losses resulting from the throttling action in conventional internal combustion engines; (3) lowering the heat lost to the exhaust by maintaining low peak gas temperatures.